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PubMed2000

HrpB2 and HrpF from Xanthomonas are type III-secreted proteins and essential for pathogenicity and recognition by the host plant.

The interaction between the plant pathogen Xanthomonas campestris pv. vesicatoria and its host plants is controlled by hrp genes (hypersensitive reaction and pathogenicity), which encode a type III protein secretion system. Among type III-secreted proteins are avirulence proteins, effectors involved in the induction of plant defence reactions. Using non-polar mutants, we investigated the role of 12 hrp genes in the secretion of the avirulence protein AvrBs3 from X. c. pv. vesicatoria and a heterologous protein, YopE, from Yersinia pseudotuberculosis. Genes conserved among type III secretion systems (hrcQ, hrcR, hrcS and hrcT) as well as non-conserved genes (hrpB1, hrpB2, hrpB4, hrpB5, hrpD5 and hrpD6) were shown to be required for secretion. Protein localization studies using specific antibodies showed that HrpB1 and HrpB4, as well as the putative ATPase HrcN, were mainly found in the soluble fraction of the bacterial cell. In contrast, HrpB2 and HrpF, which is related to NolX of Rhizobium fredii, are secreted into the culture medium in an hrp-dependent manner. As HrpB2, but not HrpF, is essential for type III protein secretion, there might be a hierarchy in the secretion process. We propose that HrpF, which is dispensable for protein secretion but required for AvrBs3 recognition in planta, functions as a translocator of effector proteins into the host cell.

Bacterial Proteins↗

PubMed1997

Analysis of the boundaries of Salmonella pathogenicity island 2 and the corresponding chromosomal region of Escherichia coli K-12.

We recently identified a pathogenicity island (SPI2) located at 30.7 centisomes on the Salmonella typhimurium chromosome. SPI2 contains genes encoding a type III secretion system whose function is distinct from that of the type III secretion system encoded by a pathogenicity island (SPI1) at 63 centisomes which is involved in epithelial cell entry. An analysis of the boundaries of SPI2 and comparison with the corresponding region of the Escherichia coli chromosome revealed that SPI2 inserted adjacent to the tRNA(Val) gene. The E. coli chromosome contains 9 kb of DNA at the region corresponding to the SPI2 insertion point which appears to be absent in S. typhimurium. The distribution of SPI1 and SPI2 was examined in various Salmonella isolates. In contrast to type III secretion system genes of SPI1, those of SPI2 are not present in Salmonella bongori, which diverged at the first branch point in the Salmonella lineage. These and other data indicate that SPI2 was acquired by a Salmonella strain already harboring SPI1 by horizontal transfer from an unknown source.

Base Sequence↗

PubMed2005

A yeast genetic system for the identification and characterization of substrate proteins transferred into host cells by the Legionella pneumophila Dot/Icm system.

The Dot/Icm system is a type IVb secretion system used by Legionella pneumophila to modulate vesicular transport in both protozoan and mammalian host cells. It has been shown that proteins and processes that are highly conserved in all eukaryotic cells are targets for some of the proteins injected by the Dot/Icm system. For example, the Legionella protein RalF was shown previously to be a Dot/Icm substrate that functions as a guanine nucleotide exchange factor (GEF) for the Arf family of eukaryotic small GTP-binding proteins. Here we show that ectopic production of the RalF protein in Saccharomyces cerevisiae interferes with yeast growth. Inhibition of yeast growth was found to be dependent on the ability of RalF to function as an Arf-GEF in vivo. The possibility that other Dot/Icm substrate proteins would have the capacity to interfere with yeast growth was used as a rationale to screen plasmid libraries containing random fragments of Legionella chromosomal DNA positioned downstream of a galactose-inducible promoter. This screen identified Legionella proteins that conferred a conditional growth defect when overproduced by yeast cultured in the presence of galactose. Most of the Legionella proteins identified were determined to be substrates of the Dot/Icm system. This screen led to the identification of a new Dot/Icm substrate protein that was called YlfA, for yeast lethal factor A. A paralogue of YlfA was identified on an unlinked region of the Legionella chromosome and this protein was also translocated by the Dot/Icm system. It was determined that a hydrophobic region near the N-terminus of the YlfA protein and an adjacent region predicted to form a coiled-coil domain were necessary for a biological activity that interfered with yeast growth. The YlfA protein did not decorate the Legionella-containing vacuole during the first 7 h of infection but could be observed on the endoplasmic reticulum (ER)-derived replicative vacuole and on punctate structures throughout the host cell at later stages. Ectopic production of YlfA in mammalian cells revealed that the N-terminal hydrophobic domain in YlfA was able to localize the protein to early secretory organelles, including endoplasmic reticulum. These studies show that yeast genetics can be exploited to identify and characterize proteins that are injected into host cells by bacterial pathogens that utilize type IV secretion systems for pathogenesis.

Animals↗

PubMed2006

Type III secretion system-associated toxins, proteases, serotypes, and antibiotic resistance of Pseudomonas aeruginosa isolates associated with keratitis.

The association between possession of toxin gene-related type III secretory system, protease profiles, O serotypes, and antibiotic resistance patterns was characterized genetically and phenotypically in 46 keratitis isolates of Pseudomonas aeruginosa. There was no significant difference in exoU or exoS prevalence among the keratitis strains. Distinct protease profiles were seen in isolates harboring either exoU or exoS genes. One hundred percent (13/13) of serotype E (O:11) strains contained type III secretion system-associated cytotoxin gene exoU. Multidrug resistance was identified in 4% of Australian and 29% of Indian isolates. None of the Australian isolates was resistant to ciprofloxacin. In general, the rate of multidrug resistance in the exoU positive cytotoxic and serotype E (O:11) strains was significantly higher than in exoS positive invasive strains (p < 0.01). The results suggest that multidrug resistance may be more commonly associated with the corneal isolates of P. aeruginosa having type III secretion system-associated cytotoxin gene exoU and belonging to serotype E (O:11) group.

ADP Ribose Transferases↗

PubMed2005

Tyrosine-phosphorylated bacterial effector proteins: the enemies within.

The tyrosine phosphorylation of proteins has a central role during signal transduction in eukaryotes. Recent progress shows that tyrosine phosphorylation is also a common feature of several effector proteins translocated by bacterial type III and type IV secretion systems. The involvement of these secretion systems in disease development is exemplified by a variety of pathogenic processes: pedestal formation (Tir of EPEC and Citrobacter), cell scattering (CagA of Helicobacter), invasion (Tarp of Chlamydia) and possibly proinflammatory responses and cell proliferation (BepD-F of Bartonella). The discovery that different bacterial pathogens use this common strategy to subvert host-cell function suggests that more examples will soon emerge.

Antigens, Bacterial↗

PubMed2004

Disruption of the phagosomal membrane and egress of Legionella pneumophila into the cytoplasm during the last stages of intracellular infection of macrophages and Acanthamoeba polyphaga.

Although the early stages of intracellular infection by Legionella pneumophila are well established at the ultrastructural level, a detailed ultrastructural analysis of late stages of intracellular replication has never been done. Here we show that the membrane of the L. pneumophila-containing phagosome (LCP) is intact for up to 8 h postinfection of macrophages and Acanthamoeba polyphaga. At 12 h, 71 and 74% of the LCPs are disrupted within macrophages and A. polyphaga, respectively, while the plasma membrane remains intact. At 18 and 24 h postinfection, cytoplasmic elements such as mitochondria, lysosomes, vesicles, and amorphous material are dispersed among the bacteria and these bacteria are considered cytoplasmic. At 18 h, 77% of infected macrophages and 32% of infected A. polyphaga amoebae harbor cytoplasmic bacteria. At 24 h, 99 and 78% of infected macrophages and amoebae, respectively, contain cytoplasmic bacteria. On the basis of lysosomal acid phosphatase staining of infected macrophages and A. polyphaga, the lysosomal enzyme is present among the bacteria when host vesicles are dispersed among bacteria. Our data indicate that bacterial replication proceeds despite physical disruption of the phagosomal membrane. We also show that an lspG mutant that is defective in the type II secretion system and therefore does not secrete the hydrolytic enzymes metalloprotease, p-nitrophenol phosphorylcholine hydrolase, lipase, phospholipase A, and lysophospholipase A is as efficient as the wild-type strain in disruption of the LCP. Therefore, L. pneumophila disrupts the phagosomal membrane and becomes cytoplasmic at the last stages of infection in both macrophages and A. polyphaga. Lysosomal elements, mitochondria, cytoplasmic vesicles, and amorphous material are all dispersed among the bacteria, after phagosomal disruption, within both human macrophages and A. polyphaga. The disruption of the LCP is independent of the hydrolytic enzymes exported by the type II secretion system.

Acanthamoeba↗

PubMed2001

Development of an MFG-based retroviral vector system for secretion of high levels of functionally active human BMP4.

We sought to develop a retroviral vector system that would produce secretion of high levels of bone morphogenetic protein (BMP)-4 by optimizing the expression construct and developing an improved retroviral vector. Replacement of the propeptide domain of BMP4 with that of BMP2 increased the secretion level of mature BMP4 protein in transduced cells. The intact BMP2 pro-peptide sequence was essential, as deletion of a small part of the propeptide sequence of BMP2 from the BMP2/4 hybrid construct diminished BMP4 expression and secretion. Addition of a hemaglutinin tag to the carboxy terminus of BMP4 abolished the bioactivity of secreted BMP4. Transduction of rat marrow stromal cells (and fibroblasts) with an MFG-based retroviral vector pseudotyped with VSV-G envelope containing this BMP2/4 hybrid expression construct led to secretion of very high levels of mature BMP4 in conditioned medium (up to 1 microg/10(6) cells/24 hours). The secreted BMP4 was biologically active, as it induced alkaline phosphatase expression in C2C12 cells. The transduced rat marrow stromal cells expressing mature BMP4 induced de novo ectopic bone formation in syngenic immune-competent rats. We have developed an MFG-based retroviral vector system that causes secretion of high levels of functionally active human BMP4 protein.

Animals↗

PubMed2005

The family of Serratia type pore forming toxins.

The Serratia marcescens hemolysin represents the prototype of a growing family of pore forming toxins. The available bacterial genome sequences reveal Serratia hemolysin homologues in additional species. However, only S. marcescens hemolysin has been studied in great molecular detail. This family of toxins has nothing in common with the pore forming toxins of E. coli type (RTX toxins), the Staphylococcus aureus alpha-toxin or the thiol activated toxin of group A beta-hemolytic streptococci (Streptolysin O). Studies on erythrocytes, eukaryotic cells and artificial black lipid membranes, have shown that the mechanism of pore formation of ShlA is different form other pore forming toxins. The S. marcescens hemolysin proteins ShlB and ShlA, exhibit protein sequence homologues in Proteus mirabilis, Haemophilus ducreyi, Yersinia pestis, Yersinia enterocolitica, Edwardsiella tarda, Photorhabdus luminescens and Xylella fastidiosa . The family of Serratia type pore forming toxins show a unique secretory mechanism which has been described as a two partner secretion system (TPSS) or type V-secretion system. Not only Serratia type pore forming toxins are secreted via TPSS but also adhesins from Bordetella pertussis, Erwinia chrysanthemi and Haemophilus influenzae. The uniqueness of the Serratia family is underlined by the fact that activation of ShlA by ShlB strictly requires phosphatidylethanolamine as a cofactor. And, quite unusual, ShlA undergoes a conformational change during activation.

Bacterial Toxins↗

PubMed1981

Studies on the mechanisms of L-dopa-induced salivary secretion.

Systemic administration of L-dopa and dopamine elicited a marked and sustained secretory response in the rat's submaxillary glands. These effects were blocked by pretreatment with phentolamine plus propranolol. Acute unilateral sympathectomy (decentralization or denervation) reduced the response to L-dopa by about 41-48%. But it left unchanged the secretory response to dopamine. Chemical sympathectomy by hexamethonium caused a similar reduction (45%) in the secretory response to L-dopa while parasympathectomy was unable to modify the salivary secretion caused by L-dopa or dopamine. Pretreatment with haloperidol reduced the salivary secretion to L-dopa in normal animals (unoperated glands), while the response to dopamine was unaffected. On the other hand, haloperidol did not alter the salivary response to L-dopa in animals with surgical sympathectomy (denervation) as compared to the same animals treated with L-dopa alone. From this study we conclude that the salivary secretion induced by L-dopa is mediated by both central and peripheral mechanisms. Dopaminergic receptors may be involved in the central effect and alpha- and beta-receptors in the peripheral response.

Animals↗

PubMed1998

Characterization of Rhizobium leguminosarum exopolysaccharide glycanases that are secreted via a type I exporter and have a novel heptapeptide repeat motif.

The prsDE genes encode a type I protein secretion system required for the secretion of the nodulation protein NodO and at least three other proteins from Rhizobium leguminosarum bv. viciae. At least one of these proteins was predicted to be a glycanase involved in processing of bacterial exopolysaccharide (EPS). Two strongly homologous genes (plyA and plyB) were identified as encoding secreted proteins with polysaccharide degradation activity. Both PlyA and PlyB degrade EPS and carboxymethyl cellulose (CMC), and these extracellular activities are absent in a prsD (protein secretion) mutant. The plyA gene is upstream of prsD but appears to be expressed at a very low level (if at all) in cultured bacteria. A plyB::Tn5 mutant has a very large reduction in degradation of EPS and CMC. Cultures of plyB mutants contained an increased ratio of EPS repeat units to reducing ends, indicating that the EPS was present in a longer-chain form, and this correlated with a significant increase in culture viscosity. Thus, PlyB may play a role in processing of EPS. Analysis of the symbiotic properties of a plyA plyB double mutant revealed that these genes are not required for symbiotic nitrogen fixation and that nodulation was not significantly affected. PlyA and PlyB are similar to bacterial and fungal polysaccharide lyases; they contain 10 copies of what we propose as a novel heptapeptide repeat motif that may constitute a fold similar to that found in the family of extracellular pectate lyases. PlyA and PlyB lack the Ca2+-binding RTX nonapeptide repeat motifs usually found in proteins secreted via type I systems. We propose that PlyA and PlyB are members of a new family of proteins secreted via type I secretion systems and that they are involved in processing of EPS.

Amino Acid Sequence↗

PubMed1999

New vaccine strategies against enterotoxigenic Escherichia coli. II: Enhanced systemic and secreted antibody responses against the CFA/I fimbriae by priming with DNA and boosting with a live recombinant Salmonella vaccine.

The induction of systemic (IgG) and mucosal (IgA) antibody responses against the colonization factor I antigen (CFA/I) of enterotoxigenic Escherichia coli (ETEC) was evaluated in mice primed with an intramuscularly delivered CFA/I-encoding DNA vaccine followed by two oral immunizations with a live recombinant Salmonella typhimurium vaccine strain expressing the ETEC antigen. The booster effect induced by the oral immunization was detected two weeks and one year after the administration of the DNA vaccine. The DNA-primed/Salmonella-boosted vaccination regime showed a synergistic effect on the induced CFA/I-specific systemic and secreted antibody levels which could not be attained by either immunization strategy alone. These results suggest that the combined use of DNA vaccines and recombinant Salmonella vaccine strains can be a useful immunization strategy against enteric pathogens.

Animals↗

PubMed2002

Bacterial persistence within erythrocytes: a unique pathogenic strategy of Bartonella spp.

The genus Bartonella comprises human-specific and zoonotic pathogens responsible for a wide range of clinical manifestations, including Carrion's disease, trench fever, cat scratch disease, bacillary angiomatosis and peliosis, endocarditis and bacteremia. These arthropod-borne pathogens typically parasitise erythrocytes in their mammalian reservoir host(s), resulting in a long-lasting haemotropic infection. We have studied the process of Bartonella erythrocyte parasitism by tracking green fluorescent protein-expressing bacteria in the blood of experimentally infected animals. Following intravenous infection, bacteria colonise a yet enigmatic primary niche, from where they are seeded into the blood stream in regular intervals of approximately five days. Bacteria invade mature erythrocytes, replicate temporarily and persist in this unique intracellular niche for the remaining life span of the infected erythrocytes. A triggered antibody response typically results in an abrogation of bacteremia within 3 months of infection, likely by blocking new waves of bacterial invasion into erythrocytes. The recent establishment of genetic tools for Bartonella spp. permitted us to identify several putative pathogenicity determinants. Application of differential fluorescence induction technology resulted in the isolation of bacterial genes differentially expressed during infection in vitro and in vivo, including an unknown family of autotransporter proteins as well as a novel type IV secretion system homologous to the conjugation system of E. coli plasmid R388. Mutational analysis of a previously described type IV secretion system displaying homology to the virB locus of Agrobacterium tumefaciens provided the first example of an essential pathogenicity locus in Bartonella. Though required for establishing haemotropic infection, it remains to be demonstrated if this type IV secretion system is necessary for colonisation of the primary niche or for the subsequent colonisation of erythrocytes.

Animals↗

PubMed2005

Additive effect on intracellular growth by Legionella pneumophila Icm/Dot proteins containing a lipobox motif.

Legionella pneumophila, the causative agent of Legionnaires' disease, utilizes a type IVB secretion system to subvert its host cells and grow intracellularly. This type IV secretion system is composed of 25 icm (or dot) genes that probably constitute parts of a secretion complex as well as more than 30 proteins that are translocated via this system into the host cells. Three of the Icm/Dot proteins (DotD, DotC, and IcmN) contain a lipobox motif at their N terminals and are predicted to be lipoproteins. Two of these lipoproteins (DotD and DotC) were found to be essential for intracellular growth in both HL-60-derived human macrophages and in the protozoan host Acanthamoeba castellanii, while the third lipoprotein (IcmN) was found to be partially required for intracellular growth only in A. castellanii. Mutation analysis of the lipobox cysteine residue, which was shown previously to be indispensable for the lipobox function, indicated that both DotC and DotD are partially functional without this conserved residue. Cysteine mutations in both DotC and DotD or in DotC together with an icmN deletion or in DotD together with an icmN deletion were found to be additive, indicating that each of these lipoproteins performs its function independently from the others. Analysis of the transcriptional regulation of both the dotDC operon and the icmN gene revealed that both had higher levels of expression at stationary phase which were partially dependent on the LetA regulator. Our results indicate that the lipoproteins of the L. pneumophila icm (or dot) system are essential components of the secretion system and that they perform their functions independently.

Acanthamoeba castellanii↗

PubMed2005

Down-regulation of stromal cell-derived factor-1alpha-induced T cell chemotaxis by a peptide based on the complementarity-determining region 1 of an anti-DNA autoantibody via up-regulation of TGF-beta secretion.

Systemic lupus erythematosus (SLE) can be induced in mice by immunizing them with a monoclonal human anti-DNA Ab that expresses a major Id, designated 16/6Id. In addition, a peptide based on the sequence of the CDR 1 (hCDR1) of the 16/6Id ameliorated the clinical manifestations of SLE in experimental models. In this study we examined the effects of treating mice with human complementary-determining region 1 (hCDR1) on the subsequent chemotaxis of T cells derived from 16/6Id-primed mice. First we demonstrated elevated levels of stromal cell-derived factor-1alpha (SDF-1alpha) in the sera of SLE-afflicted mice and in the sera and lymphoid tissues of 16/6Id-immunized BALB/c mice shortly after the immunization. We then found that administration of hCDR1 to 16/6Id-immunized mice specifically down-regulated SDF1alpha-induced T cell chemotaxis through fibronectin and collagen type I. This was accompanied by diminished SDF1-alpha-induced T cell adhesion and ERK phosphorylation. Treatment with hCDR1 up-regulated TGF-beta secretion, which, in turn, inhibited the murine T cell adhesion to and chemotaxis through fibronectin as well as their ERK phosphorylation. Thus, the secretion of TGF-beta after treatment of 16/6Id-immunized mice with hCDR1 plays an important role in the down-regulation of SDF-1alpha-mediated T cell activation and the interactions with extracellular matrix moieties observed in the present study.

Animals↗

PubMed2004

The bacterial type III secretion system-associated pilin HrpA has an unusually long mRNA half-life.

Secondary structures affect mRNA stability and may play a role in protein secretion. We have studied the mRNA of hrpA, which codes for the major structural unit of the type III secretion system-associated pilus of Pseudomonas syringae pv. tomato, Erwinia carotovora and Pseudomonas syringae pv. phaseolicola. We show that hrpA mRNA has an unusually long half-life, approximately 33-47 min. We mapped regions in the transcript that affected hrpA mRNA accumulation. Apparently, sequences at both 5' and 3' ends affect accumulation. Altering the hypothetical, stable GC rich loop structure in the 3' end of the transcript decreased transcript levels.

Bacterial Proteins↗

PubMed2003

SPARC inhibits epithelial cell proliferation in part through stimulation of the transforming growth factor-beta-signaling system.

Secreted protein, acidic and rich in cysteine (SPARC) is a multifunctional secreted protein that regulates cell-cell and cell-matrix interactions, leading to alterations in cell adhesion, motility, and proliferation. Although SPARC is expressed in epithelial cells, its ability to regulate epithelial cell growth remains largely unknown. We show herein that SPARC strongly inhibited DNA synthesis in transforming growth factor (TGF)-beta-sensitive Mv1Lu cells, whereas moderately inhibiting that in TGF-beta-insensitive Mv1Lu cells (i.e., R1B cells). Overexpression of dominant-negative Smad3 in Mv1Lu cells, which abrogated growth arrest by TGF-beta, also attenuated growth arrest stimulated by SPARC. Moreover, the extracellular calcium-binding domain of SPARC (i.e., SPARC-EC) was sufficient to inhibit Mv1Lu cell proliferation but not that of R1B cells. Similar to TGF-beta and thrombospondin-1, treatment of Mv1Lu cells with SPARC or SPARC-EC stimulated Smad2 phosphorylation and Smad2/3 nuclear translocation: the latter response to all agonists was abrogated in R1B cells or by pretreatment of Mv1Lu cells with neutralizing TGF-beta antibodies. SPARC also stimulated Smad2 phosphorylation in MB114 endothelial cells but had no effect on bone morphogenetic protein-regulated Smad1 phosphorylation in either Mv1Lu or MB114 cells. Finally, SPARC and SPARC-EC stimulated TGF-beta-responsive reporter gene expression through a TGF-beta receptor- and Smad2/3-dependent pathway in Mv1Lu cells. Collectively, our findings identify a novel mechanism whereby SPARC inhibits epithelial cell proliferation by selectively commandeering the TGF-beta signaling system, doing so through coupling of SPARC-EC to a TGF-beta receptor- and Smad2/3-dependent pathway.

Animals↗

PubMed2005

Insights into genome plasticity and pathogenicity of the plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria revealed by the complete genome sequence.

The gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria is the causative agent of bacterial spot disease in pepper and tomato plants, which leads to economically important yield losses. This pathosystem has become a well-established model for studying bacterial infection strategies. Here, we present the whole-genome sequence of the pepper-pathogenic Xanthomonas campestris pv. vesicatoria strain 85-10, which comprises a 5.17-Mb circular chromosome and four plasmids. The genome has a high G+C content (64.75%) and signatures of extensive genome plasticity. Whole-genome comparisons revealed a gene order similar to both Xanthomonas axonopodis pv. citri and Xanthomonas campestris pv. campestris and a structure completely different from Xanthomonas oryzae pv. oryzae. A total of 548 coding sequences (12.2%) are unique to X. campestris pv. vesicatoria. In addition to a type III secretion system, which is essential for pathogenicity, the genome of strain 85-10 encodes all other types of protein secretion systems described so far in gram-negative bacteria. Remarkably, one of the putative type IV secretion systems encoded on the largest plasmid is similar to the Icm/Dot systems of the human pathogens Legionella pneumophila and Coxiella burnetii. Comparisons with other completely sequenced plant pathogens predicted six novel type III effector proteins and several other virulence factors, including adhesins, cell wall-degrading enzymes, and extracellular polysaccharides.

Adhesins, Bacterial↗

PubMed2005

Comparative genomic analysis of the pPT23A plasmid family of Pseudomonas syringae.

Members of the pPT23A plasmid family of Pseudomonas syringae play an important role in the interaction of this bacterial pathogen with host plants. Complete sequence analysis of several pPT23A family plasmids (PFPs) has provided a glimpse of the gene content and virulence function of these plasmids. We constructed a macroarray containing 161 genes to estimate and compare the gene contents of 23 newly analyzed and eight known PFPs from 12 pathovars of P. syringae, which belong to four genomospecies. Hybridization results revealed that PFPs could be distinguished by the type IV secretion system (T4SS) encoded and separated into four groups. Twelve PFPs along with pPSR1 from P. syringae pv. syringae, pPh1448B from P. syringae pv. phaseolicola, and pPMA4326A from P. syringae pv. maculicola encoded a type IVA T4SS (VirB-VirD4 conjugative system), whereas 10 PFPs along with pDC3000A and pDC3000B from P. syringae pv. tomato encoded a type IVB T4SS (tra system). Two plasmids encoded both T4SSs, whereas six other plasmids carried none or only a few genes of either the type IVA or type IVB secretion system. Most PFPs hybridized to more than one putative type III secretion system effector gene and to a variety of additional genes encoding known P. syringae virulence factors. The overall gene contents of individual PFPs were more similar among plasmids within each of the four groups based on T4SS genes; however, a number of genes, encoding plasmid-specific functions or hypothetical proteins, were shared among plasmids from different T4SS groups. The only gene shared by all PFPs in this study was the repA gene, which encoded sequences with 87 to 99% amino acid identityamong 25 sequences examined. We proposed a model to illustrate the evolution and gene acquisition of the pPT23A plasmid family. To our knowledge, this is the first such attempt to conduct a global genetic analysis of this important plasmid family.

DNA Helicases↗